The invention concerns a multifunction probe for aircraft, which probe makes it possible in particular to measure the total pressure Pt and the total temperature Tt of an air flow surrounding the aircraft.
The measurement of these two parameters, total temperature and total pressure, helps to determine the actual velocity of the aircraft. Advantageously, the multifunction probe furthermore comprises means for measuring the static pressure Ps and the angle of incidence α of the air flow surrounding the aircraft. All the parameters necessary for determining the modulus and the direction of the velocity vector of the aircraft are thus available.
French patent application FR 2 802 647 filed on Dec. 17, 1999 in the name of THOMSON-CSF describes such a probe comprising a Pitot tube for measuring the total pressure Pt of the air flow and means for measuring the total temperature Tt in the form of a first channel whose air inlet orifice substantially faces the flow and of a second channel comprising a temperature sensor. The second channel bleeds off part of the air circulating in the first channel. In the embodiment described in French patent application FR 2 802 647, the Pitot tube and the first channel belonging to the means for measuring the total temperature Tt are substantially parallel and disposed in the vicinity of one another.
In practice, the first channel is advantageously disposed above or below the Pitot tube but not on one of its sides. This disposition makes it possible for the means for measuring total pressure Pt and the means for measuring total temperature Tt not to mutually disturb one another when the angle of incidence of the air flow, situated in the vicinity of the probe, is modified. On the other hand, this disposition tends to increase the projection of the probe with respect to the skin of the aircraft. Specifically, it is necessary for the air inlet orifices of the Pitot tube and of the first channel both to be situated outside a boundary layer situated in the immediate vicinity of the skin of the aircraft and in which the air is unsuitable for a good measurement of temperature or pressure.
The increase in the projection gives rise to greater fragility of the probe that would have to be alleviated by increasing the dimensions of the mast or of the airfoil carrying the Pitot tube and the first channel. The invention makes it possible to avoid this defect by reducing the projection of the probe.
Moreover, the probes mounted on aircraft are subjected to considerable temperature variations and, sometimes, to conditions under which ice may develop, in particular inside the Pitot tube or the channels allowing the measurement of total temperature Tt. The ice disturbs the measurements and, to avoid it, the probe comprises means for warming itself. These means comprise, in general, a wire warming the probe through the joule effect. This wire is coiled in the walls of the Pitot tube and in that of the channels allowing the measurement of total temperature. To produce the heating wire, use is commonly made of an electrical conductor comprising an iron and nickel alloy shrouded in a mineral insulant such as alumina or magnesia. The insulant is itself shrouded in a nickel or inconel sheath allowing the wire to be brazed to the body of the probe. Before the brazing operation, the heating wire is formed for example by winding it around cylindrical mandrels comprising reference marks making it possible to position the heating wire on the mandrels. When producing the form of the heating wire for a probe such as described in French patent application FR 2 802 647, it is impossible to wind a heating wire on two parallel mandrels. One of the mandrels then has to be offset from the axis in order to perform the operation of shaping the heating wire. Subsequently, the two mandrels are brought back parallel to one another to give the heating wire its definitive form. The latter operation of moving the mandrels is traumatic for the heating wire since it gives rise to torsional stresses in the heating wire. There is a risk that these stresses may fracture the sheath of the heating wire and consequently may reduce its reliability.
To alleviate this problem, it is possible to use two separate heating wires, one to warm the Pitot tube and the other to warm the first channel of the means for measuring total temperature. This solution is not desirable since it multiplies up the electrical connections of the probe with the aircraft on which it is mounted.
The invention makes it possible to produce a probe measuring the total pressure Pt and the total temperature Tt, which probe is equipped with a single heating wire. The inter-disposition of the various elements of the probe makes it possible to avoid any abnormal torsion of the heating wire.